Automatic telephone system.



W. T. POWELL.

AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED HOW-28, I9I3. 3,1 53%, Patented Dec, 1.91s.

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APPLICATION FILED NOV- 28, I913- Patented Dec. 28, 1915.

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T. POWELIQOF CHICAGO, ILLINOIS, ASSIGN'OR, T0 AUTOMATIG ELECTRICQOMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC TELEPHONE SYSTEM.

To all whom it may concern Be it known that I, WINFRED T. POWELL, acitizenof the United States of America, and residentof Chicago, Cookcounty, Illinois, have inventedcertain new and useful Improvements inAutomatic Telephone Systems, of which the following is a specification.1

My invention relates toimprovements in automatic telephone systems, andhas for its object the prevention of trunk lines being unnecessarilytied up after a connection has been release In the ordinary two-wiresystem each line" is provided with a line switch, which line switch isprovided with a line relay normally bridged across the line, so that assoon as a subscriber removes his receiver from the hook, this relay isenergized'and causes the line switch to operate to seize a trunk. Whenconnection is made with a line, a

- bridge-cut-oif relay is provided for cutting off or opening this linerelay bridge and thus prevent the line switch from operating when thecalled-subscriber responds. Now it the calling subscriber hangs up hisreceiver-before the called subscriber, he releases all of the switches,and as soon as the connector breaks connection with the called subscrib:ers line, the bridge-cut-off relay falls back and closes the bridgethrough the line relay, with the result that the line switch of thecalled line is operated and occupies a trunk until the'called subscriberhangs up his receiver.

The object of my invention is to prevent.

the line switch of the called line from operating in this manner andthus prevent a trunk line being unnecessarily tied, up between the timewhen the calling and called subscribers hang up their receivers.

These and other objectsof my invention;

Specification of Letters Patent. P t t 23, 1e15, ApplicationflledNovember 28,1913.

Serial No. 808,495.

gether with its individual-switch G at the central ofiice, a masterswitch D, a connector H, the called subscribers line switch C and thecalled substation A; It will be readily understood by those versed inthe art that so-called selector switches may be inserted in thesystem,thereby increasing the capacity of the exchange without departing fromtheprinciplesrof my invention. The so'-called selectorswitches may be ofa type similar to those disclosed in British patent to T. G. Martin No.1419 of 1910.

The subscribers substation A is of any suitable or approved type andcomprises the usual receiver 2, transmitter 3, switch hook 4, ringer 5and condenser 6. Being an automatic substation it is also provided withan impulse transmitter or calling device,

which is here represented by a pair of impulse springs 7 and8 and animpulse Wheel 9, which latter is assumed to be controlled through themedium of a finger hole dial made separate instead of being combined in.

a single structure. The circuits, of course, are slightly modified tooperate in a system embodying my invention. This line switch comprises,among other details,fa plunger (not shown) attached to the end of asocalled plunger arm 10 which is controlled by the operating magnetll.The magnet 11 comprises two windings, namely, the

pull-in winding 12 and the holding or cutofi Winding 13. The winding 12operates both the plunger arm 10 and the cut-01f enough only to operatethe armature 14 and to hold the plunger arm 10 in an operated positionafter it has once been operated by the pull-in winding 12., The circuitof the pull-in winding 12 is controlled by the relays 15 and 16, both ofwhich I preferably make slow acting, 6., they are slow to deenergizeafter their energizing circuit has armature 14, while the winding 13 isstrong been broken. When the plunger arm is operated, the plunger isforced into a bank of contact springs, forcing the springs 17, 18, 19-and 20 into engagement with the springs 21. 22, and '2 respectively.Although only one set of springs (17-2 1) is shown, each line switchprovided with a plurality of said sets, each set forming the terminal ofa trunk line leading to a connector switch H. Each trunk line isconnected inmultiple to the corresponding springs of all the switches ofthe group which is controlled by the master switch D.

The line switch C is controlled through the medium of the line relay 15,as will be hereinafter more fully explained.

Themaster switch D is of the same general type as that disclosed inBritish patent to R. lV. James No. 26,301 of 1906. being, however. ofthe particular type disclosed in British patent to T. G. Martin of 1910,

above referred to. The function of the master switch, as is well known,isto ma ntain the plungers of all the idle line switches in position toengage the terminal of an idle trunk line.

The connector switch H is of the same general character as thatdisclosed in United States Letters Patent No. 815.176, granted March 13.1906, to Keith, Erickson and Erickson. the circuits. however, beingmodified to adapt the switch to operate in a system in which the centraloffice apparatus is controlled bv impulses delivered over the two sidesof the line in series. The connector is providedwith a shaft (not shown)carrying the wipers 25. 26 and 27. The shaft is controlled by thevertical magnet 28 and the rotary magnet 29. Theusual side switchcomprising the wipers 30, 31, 32 and 33 is controlled by the privatemagnet 34 in the usual well-known manner.

- The magnet 35 is the usual release magnet.

The operations of the switch are controlled through the medium of thedouble-wound line relay 36, through which the calling subscriberreceives talking current. The called subscriber receives talking currentthrough the-so-called back-bridge relay 37. The ringing relay 38 is themeans through which ringing current is applied to the called line. 1

The substation A" and the line switch C (Fig. 2) are similar in allrespects to the substation A and the line switch C. For the purpose ofsupplying battery current foroperating the central ofiice apparatus, andfor talking purposes, there is shown a battery B having one terminalgrounded at G. The busy signaling machine, L, as represented herein,comprises an induction coil or transformer, the primary winding of whichis included in a local circuit with a battery and an interrupter.Through the medium of this interrupter an intermittent currentis'supplied to the primary.winding which induces an alternating currentinv the secondary wind.- ing, whereby when said winding isconnecl edwith the subscribers line, a buzzing sound is heard in the receiver.

Having given a general description of the apparatus involved in thesystem, and in order to give a complete understanding of my invention, Iwill now describe how' the subscriber at substation A may call thesubscriber at the substation A. Upon the removal of the receiver fromthe switch hook at the substation A preparatory to making a call, anenergizing circuit is closed through the line relay 15 of the lineswitch C. This circuit extends from ground G through the springs 39 andit), over the line 12, through the substation A, line 41, springs 59 and60 and the line relay 15 to the battery B, thence through battery B toground. The line re: lay 15, upon energizing, operates to close thecircuit'of-the pull-in winding 12. This circuit extends from ground Gthrough the slow acting does not fall back immediately,

however, but holds the plunger arm in an operated position until aholding ground is supplied to the holding winding 13 from the connectorH. The engagement of the springs 17 and 20 with the springs'21 and 24,respectively, extends the subscribers line to the line relay 36 of theconnector H. The line relay 36 ofthe connector switch H is thereupon 4energized, closing a circuit through the slow acting relay 50. Thiscircuit extends from ground G through the contact of springs 52 and 58and the relay 50 to the battery B. The relay 50, upon energizing, closesthe above-mentioned circuit for the holding winding 13. The said circuitextends from ground Gr through the contact of springs 54, bank springs22 and 18 and the holding winding 13 to the battery B. The winding 13,upon nergizing, holds the armature 14 and the plunger arm 10 in.

their operated positions after the circuit of the pull-in winding isbroken by the opening of the springs 46 and 17 of the line relay- 15.The deenergiza'tion of the line relay 15 also closes a circuit throughthe slow acting relay 16. The said circuit extends from ground Grthrough the contact of springs 54, bank springs 22 and 18, springs 49and the relay 16 to the battery B. The energizameat/e At the same timethat the circuit for the relay 16 is closed, a guarding ground potentialis extended to the connector private bank contacts 55, which guards thesubstation A against being seized by a connectorswitch. Theenergiz'ation of the relay 50 also prepares a circuit for the verticalmagnet 28 by bringing into engagement the springs 56 and 57 and opensthe circuit of the release magnet at the springs 57 and 58.

The calling subscriber now operates his calling device for the firstdigit 2 of the called number, wherebythe substation impulse springs 7and 8 are operated twice momentarily, each time breaking the circuit ofthe connector line relay 36; The relay 50 of the connector being slowacting does not deenergize during the momentary interruptions of itscircuit by the line relay 36, and consequently each time the latterdeenergizes, an impulse is transmitted through the vertical magnet 28.This circuit extends from ground G through the contact of springs 52 and51, springs 57 and 56, relay 61', vertical magnet 28 and the side switchwiper 30 (in first position) to the battery B. The vertical magnet 28receives two impulses over this circuit and operates to raise the switchwipers 25, 26 and 27 to a position opposite the second level of bankcontacts. The relay 61, which is included in series a with the verticalmagnet, remains energized during the entire time that impulses are beingtransmitted through it and operates toclose the circuit of the privatemagnet 34. The circuit for the private magnet 34 ex tends from ground Gthrough the contact of springs 62 and 64 and the said magnetto thebattery B. After the last impulse is delivered, the relay 61 opensthecircuit of the private magnet 34, which, upon de'einergiz- 'ing,permits the side switch to advance from first to second position. Themovement of the side switch wiper 30 "from first'to second positlontransfers the battery connection from the vertical-magnet 28 to therotarymagnet 29.

The calling subscriber now operates his calling device for the lastdigit 0, in response to which the connector line relay operates totransmit ten impulses through the rotary magnet 29 in series with. therelay 61 wherebyv the shaft wipers arerotated onto the contacts of thedesired line. '1 The said circuit extend's'from ground G through thecontact of springs 52 and 51, springs 57 and 56, relay 61, springs 65and 66, rotary ma'gnet 29 and-the side switch wiper 30 (in sec- Therelay 61 operates in response to the impulses for this digit in the samemanner as for the previous digit to cause the private magnet 34 toadvance the side switchone more posicalled substati tion, 2'. e., fromsecond to third position. By the engagement of the side switch wipers 32and 33 with their third-position contact The circuit for thebridge-cut-ofi winding 67 extends from ground G through the side switchwiper 31 (in third position), private wiper 26, conductor 68, springs 69and the cut-ofi' winding 67 to the battery lead 100. The slow actingrelay 70 of the line switch C" is also energized at this time, but theoperation of said relay is functionless at this time. A guarding groundpotential is supplied to the connector private bank contact 71 of thecalled line'which prevents the same from being seized by some otherconnector switch. By the engagement of the .side switch wiper 30 withits third-position contact point, the circuit of the ringer relay 38 isclosed. This circuit extends from ground G through the interrupter 72,relay 38, contact of springs 73 and the side switch wiper 30 (in thirdposition) to the battery B. The ringer relay disconnects the callingline from the called line and bridges the ringing current generator Racross the called line to signal the called subscriber; The ringer re- 1I lay is energized only intermittently through the medium of theinterrupter 72. Upon the response of, the called subscriber, his line isprovided with talking current through the windings of the back-bridgerelay 37, which relay, upon energizing, closes the circuit through theringer cut-off relay 74. The said circuit extends from ground G throughthe side switch wiper 31 (in third position),

contactvof springs 75 and the said relay 74 to the battery B. The relay74, upon energizing, interrupts the circuit of the ringer relay 38 atthe springs 73 and closes a locking circuit for itself through thesprings 7 6 independent of the springs 75. After the conversation iscompleted, the connection is released by the hanging up of'the receiverat the calling substation in the following manner: When the receiver atthe substation A is restored to the switch-hook, the

separation of the hook-switch springs destroys the energizing circuit ofthe connector line relay'36. The relay 36 is thereupon deenergized, andopens the circuit of the relay 50. The relay v50, upon denergizing,comarm 10 to return to normal csition.

Heretofore in systems otthis character, if the calling subscriber hunt ahis receiver and thus released a connection betore the called subscriberhung up his receiver, then the circuit of the pull-in winding of thecalled subscribers line switch would be closed and this switch operatedto seize a trunk. As before stated, the object of my invention is toprevent a trunk being seized and occupied in this manner. This isaccomplished as follows: Assuming that the calling subscriber hasreplaced his receiver upon the receiver hook, and that the calledsubscriber still has his receiver oil' the receiver hook. The connectorswitch, upon releasing, opens the circuits of the cut-off winding 67 andthe slow acting relay 70 of the line switch C. The cut-oft winding 67,upon deenergizing, closes an energizing circuit through the line relayof the said line switch, thus causing it to energize. The relay 70 beingslow acting does not deenergize immediately when, its circuit is broken,and consequently the circuit of the pull-in winding 81 is retainedopened at the springs 82 as long as said relay is energized.

The line relay 80, upon energizing, closes a holding circuit for theslow acting relay 70. The said circuit extends from ground G through thecontact of springs 83, 84 and 85,'springs 86 and the relay 70 to thebattery lead 100, thus retaining the relay 70 energized, which in turnretains the circuit of the pull-in winding 81 openedat the springs 82.The circuit of the pull-in winding being thus held open, the line switchC is prevented from operating and thus occupying a trunk. If the calledline had been busy when the connector attempted to make connectiontherewith, the busy signal would be sent back to the calling subscriberin the well-known manner. This, however, forms no part of my presentinvention and is well understood in the art, and a detailed descriptionof the same is accordingly thought unnecessary.

While I have illustrated my invention in connection with one particulartype of automatic system, it will, of course, be understood that it iscapable of use with many other forms of systems and is equally as welladapted for use in connection with semi-automatic systemsthat is,systems in which a manual link circuit is employed in combination withautomatic means for cstablishing a connection between two subscriberslines.

It will thus be seen that I have provided very efficient means forpreventing. the line relay for saidswitch normally hr switch of thecalled line being unnecessaril operated to seize a trunk when the callinsubscriber hangs up his receiver and releas s the connection before thecalled subscriber has hung up his receiver.

What I claim as my invention is:

1'. In telephone system. a subscril l. line, a line switch individualthereto, a line across'said line, a trip magnet controller. said linerelay, a lJIlClQ'G CUE-Olf relay, means for energizing said cut-oftrelay when con nection is made with said line. means controlled therebyfor opening the circuit oi.

said line relay, a second relay adapted to be e energized in multiplewith said cut-off relay, and a normally closed contact in the circuit ofsaid trip magnet controlled by said second relay.

2. In a telephone system. a subscribers line, a line switch individualthereto, a line relay for said switch normally brid ed across said line,a trip magnet controlled by said line relay, a bridge-cut-ofi relay,means for energizing said cut-oil relay when connection is made withsaid line, means con trolled thereby for opening the circuit of saidline relay, a second relay adapted to be energized in multiple with saidcut-oil relay. a normally closed contact in the circuit of said tripmagnet controlled by said second relay, and a locking circuit for saidsecond relay for maintaining it energized after the first energizingcircuit is broken.

3. In a telephone system, a calling and a called line, a line switch foreach line including a line relay normally bridged across the line anda-trip magnet controlled thereby, means for cutting off the linerelay onthe called line when connection is extended thereto. and means includinga relay for preventing said trip magnet of the called line switchenergizing when the connection is disconnected before the calledsubscriber hangs up his receiver.

4. In a telephone system, a line, a circuit controller for said line,means for extending a connection to said line and for disconnectingtherefrom, trunking equipment responfor making a call from said line,means for rendering said trunking equipment nonresponsive-to saidcircuit controller and for maintaining it so after the connection isdiscontinued.

5. In a telephone system, a calling line, a

' called line, means for connecting the two and means for releasing theconnection,

trunking equipment associated with the called line for enabling thecalled line to 7 make a call, said equlpment responsive to the closureof the circuit of the called line, means for rendering said equipmentinoperative-when the second line is called, and means for maintainingsaid equipment nonresponsive to the closure of the circuit of the secondline after the first line releases the connection.

6. in a telephone system, a line, automatic trunking equipment forextending a connection from said line, a relay for said line forcontrolling said equipment, a circuit for energizing said relay when acall is initiated, said equipment operated over said line When the lineis closed, means in theline for closing said circuit, and means forrendering said equipment inoperative when the line is called and formaintaining it inoperative after the calling line releases.

7. In a telephone system, a calling line, a called line, a relay for thecalled line, trunking equipment controlled therebyfor extending callsfrom the called line means for WKNFRED 'l. POWELL.

Witnesses: I

G. A. YANOCBOWSKI, HARRY E. Hnnsnz,

